How low power can I go while retaining use of Timer0 with ATmega328p/ATtiny85?

I am working on a watch with a small ssd1306 display. I am using the rocketscream library GitHub - rocketscream/Low-Power: Low Power Library for Arduino to put the Arduino in sleep to save power.
Timer0 must be disabled or else it will interrupt every millisecond.
I tried turning off interrupts with noInterrupts() before sleeping and turning them on again after, while keeping timer0 on. This did not work. It might have just been my code but i don't think so. If this would work, please tell me. From what I've found out, interrupts will queue up while interrupts are disabled and then process again once they are turned off. does the timer0 interrupt carry a data point with elapsed millis or does the interrupt just add one to a counter?

If that isn't an option, how low power can I go while keeping timer0 on?
What stuff can i disable?

You could start by reading this: Gammon Forum : Electronics : Microprocessors : Power saving techniques for microprocessors

The lowest voltage is 1.8 volts but the clock has to be reduced to max 4MHz to match this.

6v6gt thanks that page looks very comprehensive.